import math, sequtils, strutils, sugar

const
  m = 10 ^ 9 + 7
let
  n = parseInt readLine stdin
  xs = newSeq.collect:
    for _ in 0 ..< n:
      let
        cd = stdin.readLine.split.map parseInt
        c = cd[0] mod m
        d = cd[1] mod m

      c.succ div 2 * d mod m

echo (sum xs) mod m